The present invention relates to video cameras, and in particular to video cameras and web cameras with image sensors capable of operating at fixed or variable frame rates.
FIG. 1 is a diagram of a prior art conventional video processing scheme 100. Frames are sequentially received from an image sensor (not shown) at Receive Frame step 110. Each frame is then sent sequentially to Pixel Correction 120 where bad pixel information is used to correct for hot or dead pixels. From there the frame is sent to Auto Focus step 130 where the frame is analyzed to determine whether the lens (not shown) needs to be adjusted to achieve best focus. If Auto Focus step 130 determines that a lens adjustment is necessary, a feedback signal is sent to motors or actuators to adjust the focal position of the lens. From there the frame is sent to Color Processing 140. Color Processing 140 will analyze the frame to determine if any color corrections are necessary. Color corrections typically include gamma correction, white balance correction and exposure correction, however various other corrections can be made to optimize the color rendition of the frame at Color Processing 140. From there, the color corrected image is sent to Compression 150 where the frame is compressed or not. Finally, the frame is sent to Display 160. Display 160 will typically display the frame on a video monitor but can also record the frame on a recording device. Alternately, instead of a display, the video can be sent to an Instant Messaging application, uploaded to a web site, or otherwise transmitted.
From FIG. 1, it is clear that conventional video processing scheme 100 requires each frame to be individually analyzed and processed before it is displayed or recorded. Such analysis and processing is computationally intensive and requires one or more fast processors to achieve smooth, uninterrupted quality video. If any single frame is delayed in the video processing scheme 100, the resulting video can stall or appear to run it slow motion. Delays are therefore undesirable for quality video.
Additionally, Auto Focus step 130 is a recursive feedback process. Auto Focus step analyzes each frame for correct focus. If Auto Focus step 130 determines that the focus needs to be adjusted, it sends a command to the lens focus motors to adjust the lens for the subsequent frames. Each subsequent frame is then analyzed to determine if further adjustments are needed. Each time an adjustment is made, there is chance that the adjustment either overshoots or under shoots the correct focus position of the lens for a particular scene. In such cases, Auto Focus step 130 will determine that another adjustment is needed. The over shooting and under shooting of the correct focus position of the lens can will cause the resulting video image appear to oscillate in and out of focus. In many applications, the oscillation of the focus is distracting and undesirable.
In low-light conditions imaging and focus are even more difficult. Since most silicon based image sensors are highly sensitive to IR light, most contemporary video imaging applications use an IR filter to reduce the IR light and shape other spectral characteristics of the scene being imaged. As a result, some of the available light is lost. In normal lighting conditions, the reduction in brightness is only nominally detrimental to focusing and imaging a scene. However, when light levels are low, there can be very little information in the imaged scene for the auto focus routine and other image processing routines to analyze. The problems with oscillating focus described above are exacerbated and other image processing routines, such as color correction and noise reduction, are frustrated.
Thus, there is a need for inexpensive and reliable method, system and apparatus to automatically adjust focus and make other image qualities corrections in video cameras without interrupting the smooth appearance of quality video streams.